Know the information
It's pivotal to be prepared before a public speaking engagement. Acquire all necessary knowledge when you're preparing and make sure you know it inside and out. Ask yourself: What am I forgetting? What should I hone in on? Why the fuck is "colonel" spelled like that?
Know the space
Become accustomed with your environment; what are the acoustics like? Be familiar with the software should you use audio-visual aids. Locate the nearest exit to run out of when someone asks a question you can't answer/you somehow find yourself in a situation where you have to pronounce "gyro."
Know your star sign
Because you should always be prepared to date at a moment's notice!!! Even if you're in the middle of a presentation!
Become familiar with your audience
Who is your target demographic? Are you pandering towards their interests? And remember, first impressions last the longest! For example, don't wear camo pants (they're unprofessional and tell your audience that you've bought an Applebee's giftcard at a gas station at 3 A.M. once) or anything too high-end like a Brooks Brothers suit (this says you're in a high enough tax bracket to have your ketchup served in a ramekin.)
Make eye contact
This makes your audience feel involved. Make sure you make eye contact with every person in your audience for three seconds at a time; 10 seconds if someone's transition lenses are just catching up.
Avoid relying on your notes too much
Constantly looking down at your notes will give the impression that you don't know your material as well as you should. If you feel like you're looking down too much just start reciting the lyrics to Queen's "Bohemian Rhapsody" and continue to do until you remember what your next speaking point is.
Allow yourself to take pauses in between your speaking points. It gives your audience the chance to register what you've just said. The appropriate pace to speak is a fair median between verbal molasses and the reading of the fine print after a radio advertisement.
If you freeze up during your presentation
Stop, drop and roll out of the room.